CVE-2026-40019 Denial of service in OX Dovecot CE
An unauthenticated attacker can cause a denial of service by sending a truncated quoted argument to the ManageSieve login process, leading to infinite CPU consumption.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-40019?
CVE-2026-40019 is a medium-severity denial of service vulnerability in Open-Xchange GmbH OX Dovecot CE, published on 28 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
An unauthenticated attacker can send a truncated quoted argument to the ManageSieve login process, which makes it spin in an infinite loop consuming CPU. This can cause degradation or denial of service for Sieve script management, and repeated connections can consume all available CPU on the server. Monitor system for abnormal CPU usage and kill the offending process. Restrict network access to the ManageSieve service to trusted clients. Update to non-vulnerable version. No publicly available exploits are known.
Weakness: CWE-400
Which versions are affected by CVE-2026-40019?
How do I fix CVE-2026-40019?
Upgrade to a fixed version.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-40019 being exploited?
There is no known exploitation of CVE-2026-40019 in the wild and no public exploit code.
Sources
Also known as ALPINE-CVE-2026-40019, DEBIAN-CVE-2026-40019, GHSA-c3mr-h4j4-h26r, UBUNTU-CVE-2026-40019.